Endothelial function is a measure of the activity of endothelial cells that line the inside of the blood vessels. These cells control blood flow by regulating the dilation of the blood vessels.

Impaired endothelial function, which is considered to be a marker for cardiovascular disease, can lead to high blood pressure or atherosclerosis, in which the arteries become clogged by plaque, increasing the risk of heart disease and stroke.

Rudolph and colleagues measured the initial endothelial function and other markers of cardiovascular disease in 24 healthy volunteers (average age of 32 years) who followed no particular diet and took no vitamin supplements.

The 14 women and 10 men then ate one of three readily available fast food meals during one week, a different meal the second week and the remaining meal the third week.

The meals consisted of a beef burger, fries, ketchup, and a lemon-flavored carbonated drink; a vegetarian burger, fries, ketchup, and a lemon-flavored carbonated drink; or a vegetarian burger plus salad, fruit, yogurt, and orange juice, the researchers report in The American Journal of Clinical Nutrition.

Unexpectedly, the researchers found that endothelial function was adversely affected within 2 and 4 hours after eating each of the three meals, with no statistically significant differences among them. Furthermore, all three meals had a negative impact on other cardiovascular disease markers as well, Rudolph said.

“When we planned the study, our hypothesis was that “healthy” components like orange juice or salad would be able to prevent impairment of endothelial function,” Rudolph noted, “But we could not show this.”

“You can not prevent the harmful effects of fast food to the vascular system if you only add ‘healthy components,’” Rudolph concluded.